Alkylation process with efficient effluent refrigeration

ABSTRACT

An alkylation process in which a recycle stream is cooled by heat exchange with the alkylation reactor effluent is disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/172,297, filed Jun. 12, 2002 now U.S. Pat. No. 6,943,276, theteachings of which are hereby incorporated in their entirety herein byreference.

FIELD OF THE INVENTION

This invention relates generally to a process for the alkylation of analkylation substrate with an alkylating agent. This invention relatesspecifically to the separation and heat exchange of the alkylationeffluent.

BACKGROUND OF THE INVENTION

The alkylation of an alkylation substrate (e.g., isoparaffin) with analkylating agent (e.g., olefin) is an exothermic reaction. Commerciallyit is practiced using a catalyst at relatively low temperatures, whichhelps raise the yield of alkylate, the valuable product. The optimumalkylation temperature depends on many factors including the choice ofcatalyst, but alkylation reactors generally run in the range of −50 to100° C. (−58 to 212° F.). The alkylation reactor effluent is usually inthat temperature range too. Thus, the effluent poses a unique technicalchallenge in three aspects—to recover the product alkylate, to utilizethe heat released by the alkylation reaction, and to recycle reactantsto the reactor at a suitable low temperature.

Prior art alkylation units try to meet this challenge by flashing thereactor effluent. This produces a vapor that contains mostly unreactedalkylation substrate. This vapor is then used like a refrigerant is usedin a refrigeration system; indeed, it is commonly called “refrigerant”.It is compressed, condensed, and then flashed. These steps provide astream which is both coolant and reactant. It is, therefore, well-suitedfor recycling to the reactor.

Unfortunately, the prior art units don't work well when the vaporcontains light components don't condense at conventional condensationconditions. These components often include (but are not limited to)hydrogen, hydrogen chloride, methane, and ethane. They are commonlycalled “noncondensables,” even though they most certainly will condenseat very high pressure, if the temperature is low enough. But compressingthe refrigerant in an alkylation process to that high of a pressure isprohibitively expensive. The costs of high-pressure equipment andutilities are simply too great.

Therefore, efficient methods are sought to recover alkylate, use theheat of reaction, and recycle unreacted alkylation substrate.

SUMMARY OF THE INVENTION

An alkylation process wherein the refrigerant is cooled by heat exchangewith the alkylation reactor effluent is disclosed. This process hasseveral advantages. One in particular occurs when the effluent containscomponents that do not condense at conventional condensation conditionsto be recycled to the alkylation reactor. This is the case when thealkylation catalyst comprises chloride and the effluent containshydrogen chloride. Then, the process disclosed herein helps to recyclelight components such as hydrogen chloride and to cut hydrogen chloridelosses, without excessive compression costs. This process is also usefulwhen direct cooling of the alkylation reactor using reactor effluent isnot practical because of the design of the alkylation reactor and/or theproperties of the reactor effluent.

In one embodiment, this invention is an alkylation process. Analkylation substrate is alkylated with an alkylating agent in a reactorto form alkylate. A reactor effluent comprising the alkylate and thealkylation substrate is recovered from the reactor. At least a portionof the reactor effluent is flashed to form a refrigerant exchanger feedcomprising the alkylate and the alkylation substrate. At least a portionof the refrigerant exchanger feed is heated in a refrigerant heatexchanger. A refrigerant exchanger effluent comprising the alkylate andthe alkylation substrate is recovered from the refrigerant heatexchanger. At least a portion of the refrigerant exchanger effluent ispassed to an effluent vapor-liquid separator. A vapor phase comprisingthe alkylation substrate and a liquid phase comprising the alkylate arerecovered from the effluent vapor-liquid separator. The vapor phase iscompressed to form a compressed stream comprising the alkylationsubstrate. At least a portion of the compressed stream is at leastpartially condensed to form a condensed stream comprising the alkylationsubstrate. In the refrigerant heat exchanger, heat is indirectlyexchanged from at least a portion of the condensed stream to the atleast a portion of the refrigerant exchanger feed in order to form achilled recycle stream comprising the alkylation substrate. At least aportion of the chilled recycle stream is recycled to the reactor. Thealkylate is recovered from the liquid phase.

Additional embodiments and advantages of this invention are described inthe detailed description.

INFORMATION DISCLOSURE

U.S. Pat. No. 5,750,818 (Mehlberg et al.) describes an alkylationprocess for cooling unreacted hydrocarbon substrate that is recycled toan alkylation reactor.

Process Economics Program Report No. 88A, Alkylation of Motor Fuels(February 1993) by Elaine J. Chang, SRI International, Menlo Park,Calif., describes alkylation processes that employ sulfuric acid andautorefrigeration.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 show embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The feedstocks for this invention are an alkylation substrate and analkylating agent. The alkylation substrate is a paraffinic hydrocarbon,such as a branched paraffin having from 4 to 6 carbon atoms. Suitableparaffinic hydrocarbons include 2-methylpropane (commonly calledisobutane), 2-methylbutane (or isopentane), 2,3-dimethylbutane,2-methylpentane, and 3-methylpentane. More than one paraffin may beused.

The alkylation substrate is alkylated with an alkylating agent. Thealkylating agent is typically an olefinic hydrocarbon containing from 2to about 6 carbon atoms. Examples of such olefins include ethylene,propylene, 1-butene, cis-2-butene, trans-2-butene, and iso-butene. Morethan one olefin may be used.

The alkylation can be performed using any suitable catalyst. Althoughthe alkylation catalyst may be a liquid such as hydrogen fluoride orsulfuric acid, the preferred catalyst is a solid or heterogeneouscatalyst. U.S. Pat. No. 6,392,114 B1 (Shields et al.), which is herebyincorporated herein by reference, describes suitable solid catalysts.The process disclosed herein is well-suited generally for a catalystthat comprises a halide. One such catalyst is a refractory inorganicoxide impregnated with a monovalent cation, especially an alkali metalcation or an alkaline earth metal cation, and whose bound surfacehydroxyl groups have been at least partially reacted with aFriedel-Crafts metal halide, as described in U.S. Pat. No. 6,392,114 B1.The alkylation reactor may be any suitable alkylation reactor. When thealkylation catalyst is a solid, a transport reactor may be used. U.S.Pat. No. 6,392,114 describes a suitable riser-reactor.

Suitable alkylation conditions include a temperature of from about −50to about 100° C. (−58 to 212° F.) and a pressure as required to maintainthe hydrocarbons present as a liquid. The pressure is in the range ofusually from about 1380 to about 4830 kPa(g) (200 to 700 psi(g)). Sincean excess of the alkylation substrate is generally provided relative tothe alkylating agent, the overall molar ratio of alkylation substrate toalkylating agent is generally from about 5:1 to about 20:1. Injection ofthe alkylating agent at a number of points in the alkylation reactor maybe used to maintain an average molar ratio that is higher than theoverall molar ratio. The alkylation reactor may be any suitable reactorsuch as a riser-reactor. The reactor and reaction conditions aregenerally chosen to achieve desired values of reactant conversion,product selectivity, and catalyst stability. However, if desired aperson of ordinary skill in the art can optimize the selection of theseparameters to affect the product recovery and recycling of components.

The alkylation reaction effluent generally contains the desired productof the alkylation (alkylate), byproducts of side reactions, andunreacted alkylation substrate. When alkylating butenes with isobutane,the alkylation reaction effluent typically comprise hydrocarbons havingfrom 1 to 12 carbon atoms, including methane, ethane, propane, propene,butanes, butenes, pentanes, pentanes, hexanes, heptanes, octanes,nonanes, decanes, undecanes, and dodecanes. Depending on the alkylationcatalyst, the alkylation reaction effluent may contain ahalogen-containing species too. The halogen-containing species istypically present in a concentration of generally greater than about 250wt-ppm halogen, and is usually from about 1000 to about 10000 wt-ppmhalogen, based on the weight of the alkylation reaction effluent.Examples of halogen-containing species include organic halides andhydrogen halides. These species include organic fluorides, organicchlorides, organic bromides, hydrogen fluoride, hydrogen chloride, andhydrogen bromide. Examples of organic halides include the products ofhalogenating the alkylating agent such as propyl chlorides and butylchlorides.

In accord with the process disclosed herein, some or all of thealkylation reactor effluent is flashed. That is, its pressure is loweredfrom the reaction pressure to a lower pressure. Although the flashingpreferably occurs at constant enthalpy, the enthalpy of the reactoreffluent may change. Since the hydrocarbons in the alkylation reactoreffluent are usually in a liquid phase, the flashing typically vaporizessome of the lighter hydrocarbons in the effluent, such as the alkylationsubstrate. The resulting reactor effluent may thus be a two-phasemixture of vapor and liquid.

The flashing also lowers the temperature of the reactor effluent. Eventhough the reactor effluent may carry with it some of the heat generatedby the alkylation reaction, the temperature of the reactor effluentafter the flashing is low enough as to permit some or all of the reactoreffluent to be used to cool another stream by indirectly exchanging heatfrom that stream. That in turn heats the reactor effluent. The streamthat is cooled is formed at least in part from a vapor phase whichitself is formed by phase separating the reactor effluent after theindirect heat exchange.

The phase separation of the reactor effluent after the indirect heatexchange takes place at a pressure of generally from about 0 to about483 kPa(g) (0 to 70 psi(g)) and at a temperature of generally from about−9 to about 32° C. (15 to 90° F.). (The pressure could also besubatmospheric, provided that suitable measures to limit or prevent airingress are taken. However, such measures are usually impractical oruneconomical.) More specifically, those conditions depend in part on thenumber of times the reactor effluent (or a liquid phase derivedtherefrom) is flashed enroute from the alkylation reactor to thealkylate product recovery section. Each stage of flashing lowers thepressure and temperature of the stream that is flashed, and therefore itis generally the case that the greater the number of stages, the smalleris the drop in pressure and temperature from stage to stage. Thus, thegreater the number of stages, the closer the pressure and temperature ofthe phase separation of the reactor effluent after the indirect heatexchange is to the pressure and temperature of the alkylation reactoritself. Thus, the phase separation with only a single stage of flashingoccurs at a pressure of generally from about 69 to about 207 kPa(g) (10to 30 psi(g)), preferably from about 103 to about 172 kPa(g) (15 to 25psi(g)), and at a temperature of generally from about 7 to about 18° C.(45 to 65° F.), preferably from about 10 to about 16° C. (50 to 60° F.).If there are two stages of flashing, this phase separation occurs at apressure of generally from about 207 to about 414 kPa(g) (30 to 60psi(g)), preferably from about 241 to about 379 kPa(g) (35 to 55psi(g)), and at a temperature of generally from about 7 to about 24° C.(45 to 75° F.), preferably from about 10 to about 21° C. (50 to 70° F.).If there are three stages of flashing, this phase separation occurs at apressure of generally from about 241 to about 483 kPa(g) (35 to 70psi(g)), preferably from about 276 to about 448 kPa(g) (40 to 65psi(g)), and at a temperature of generally from about 18 to about 32° C.(65 to 90° F.), preferably from about 21 to about 29° C. (70 to 85° F.).The vapor phase that results from this phase separation is enriched inthe alkylation substrate relative to the reactor effluent, and theresultant liquid phase is depleted in the alkylation substrate.

The stream that is cooled by indirect heat exchange with the reactoreffluent is sometimes referred to herein as the refrigerant, because itis used in the process disclosed herein in a way similar to how arefrigerant is used in a refrigeration system. The refrigerant, which isformed at least in part from vapor phase from the phase separation, iscompressed. After being compressed and prior to being cooled in theindirect heat exchange step, the refrigerant is at least partiallycondensed using a condenser. Usually the condenser is either a water- orair-cooled heat exchanger, but other coolants for the condenser arepossible. For example, the condenser coolant may be the workingrefrigeration fluid of an external refrigeration unit, or it may be astream in the product recovery section that requires reboiling.

The indirect heat exchange then itself may partially condense, completethe condensation of, or lower the temperature of, the refrigerant. Anysuitable indirect heat exchanger may be used. After the indirect heatexchange step, the temperature of the refrigerant is generally fromabout 2 to about 11° C. (3 to 20° F.) and preferably from about 3 toabout 8° C. (5 to 15° F.) above the temperature of the phase separationof the reactor effluent after the indirect heat exchange. The pressureof the refrigerant is generally sufficient to achieve the desired extentof condensation.

After the indirect heat exchange, the refrigerant is either a two-phase,vapor-liquid mixture containing components that did not condense(partially condensed) or a single liquid phase (totally condensed).Generally, the refrigerant has been chilled by the indirect heatexchange to as low a temperature as can be practically attained.Although the refrigerant contains mostly the alkylation substrate whichis almost entirely condensed after the indirect heat exchange, thereactor effluent and hence the refrigerant may contain components thatdo not condense either in the condensation step or in the indirect heatexchange step. These components have not condensed because theirconcentration in the refrigerant has risen or is otherwise beyond thelevel of their solubility in the refrigerant at the conditions oftemperature and pressure after the refrigerant has been indirectly heatexchanged with the reactor effluent. These uncondensed componentsusually have fewer carbon atoms than the alkylation substrate. Theseuncondensed components comprise most of any vapor phase that is presentafter the indirect heat exchange step, except for any equilibrium (ornear-equilibrium) concentration of the alkylation substrate owing to thevapor phase being in contact with the liquid phase.

In some instances, these uncondensed components in the refrigerant arepreferably returned to the alkylation reactor. For example, hydrogenchloride in the refrigerant may not condense at the outlet conditions ofthe indirect heat exchange step, but if the alkylation takes place inthe presence of a chloride-containing solid catalyst it would bepreferred that the hydrogen chloride condensed. If the hydrogen chloridewould condense, then if the liquid phase is recycled to the alkylationreactor the hydrogen chloride would be returned as well. So, in such acase, preferably the conditions of the refrigerant after the indirectheat exchange are sufficient to keep in solution in the liquid phase atleast 99% and more preferably all of the hydrogen chloride in therefrigerant. Any uncondensed hydrogen chloride would be lost from therefrigerant and would have to be replaced by adding makeup chloride tothe alkylation reactor, unless it is otherwise recovered and returned tothe process.

The optimum amount of condensation for a component in the refrigerantthat is preferably returned to the alkylation reactor depends on aneconomic balancing of the costs of not condensing the component with thecosts of condensing the component. The costs of not condensing acomponent such as hydrogen chloride would include the costs of addingmakeup chloride and of disposing of lost hydrogen chloride. These costsare offset by the costs of the high-pressure equipment and of theutilities needed to compress the refrigerant to a sufficiently highdischarge pressure to condense the component. A person of ordinary skillin the art can determine this optimum.

In other instances, the uncondensed components in the refrigerant arepreferably not returned to the alkylation reactor, as in the case ofparaffins lighter than or having fewer carbon atoms than the alkylationsubstrate. Examples include propane, ethane, and methane when isobutaneis the alkylation substrate. Such components are preferably maintainedin the vapor phase and are separated from the alkylation substrate bydistillation or phase separation prior to recycling the alkylationsubstrate to the alkylation reactor.

The liquid phase resulting from the phase separation of the alkylationreactor effluent after the indirect heat exchange may itself be flashedand then phase-separated one or more times. Each subsequent flash andphase separation lifts more and more of the alkylation substrate andother components from the liquid phase. So, each resulting vapor phaseis enriched in alkylation substrate, and each resulting liquid phase isdepleted in alkylation substrate, relative to the liquid phase that isflashed. The resulting vapor phase(s) can be compressed in one or morecompression stages and can be ultimately combined with the vapor phasefrom the initial phase separation of the alkylation reactor effluent. Aperson of ordinary skill in the art can optimize the number of flashing,phase separation, and compression stages, and their operatingconditions, in order to achieve a desired recovery of alkylationsubstrate and alkylate and with a view toward minimizing utilities costsfor a given expenditure in capital equipment. With two stages offlashing (and compression), the second phase separation occurs at apressure of generally from about 21 to about 117 kPa(g) (3 to 17psi(g)), preferably from about 55 to about 83 kPa(g) (8 to 12 psi(g)),and at a temperature of generally from about −4 to about 13° C. (25 to55° F.), preferably from about −1 to about 10° C. (30 to 50° F.). Withthree stages of flashing, the second phase separation occurs at apressure of generally from about 138 to about 276 kPa(g) (20 to 40psi(g)), preferably from about 172 to about 241 kPa(g) (25 to 35psi(g)), and at a temperature of generally from about 4 to about 18° C.(40 to 65° F.), preferably from about 7 to about 16° C. (45 to 60° F.).With three stages of flashing, the third phase separation occurs at apressure of generally from about 0 to about 69 kPa(g) (0 to 10 psi(g)),preferably from about 7 to about 34 kPa(g) (1 to 5 psi(g)), and at atemperature of generally from about −9 to about 2° C. (15 to 35° F.),preferably from about −7 to about −1° C. (20 to 30° F.). In this lattercase the pressure could be subatmospheric, subject to the earliercomments herein concerning air ingress.

The process disclosed herein can be more fully understood by referenceto FIGS. 1 and 2. For clarity and simplicity, some items associated withthe operation of the embodiments of the invention have not been shown.These items include flow and pressure control valves, heaters, pumps,compressors, heat exchangers, temperature and pressure monitoringsystems, vessel internals, etc., which may be of customary design. FIGS.1 and 2 are not intended to limit the scope of the invention as setforth in the claims. In addition, the description of FIGS. 1 and 2 iswritten in terms of isobutane as the alkylation substrate, a mixture ofbutene isomers as the alkylation agent, and hydrogen chloride as thehalogen-containing species in the reactor effluent. However, the choiceof these reactants and this halogen-containing species is not intendedto limit the scope of the invention as set forth in the claims.

Referring now to FIG. 1, a mixed butenes feedstock enters alkylationreactor 10 through line 12. The butenes may be introduced into thereactor 10 at more than one point. A stream containing fresh and recycleisobutane as the alkylation substrate enters reactor 10 through line 14.The alkylation reactor uses a solid catalyst employing a chloride. Thealkylation reactor effluent contains alkylate, isobutane, propane,ethane, methane, and hydrogen chloride. The C₁–C₃ paraffins may haveentered the reactor with the feedstocks or may have been formed asalkylation byproducts. The effluent may even contain some hydrogen dueto catalyst regeneration.

The alkylation reactor effluent flows through line 16 and splits intotwo portions. One portion flows through line 17 and flashes acrossexpansion valve 18, which lowers that portion's pressure andtemperature. The flashed portion is a two-phase vapor-liquid mixturethat flows through line 20 into refrigerant heat exchanger 22. Byindirect heat exchange, the flashed portion removes heat from the streamflowing through line 38, thereby heating this portion of the reactoreffluent. The heated portion is still a two-phase vapor-liquid mixture.The flows through line 24, combines with the stream flowing in line 70,flows through line 25, and enters vapor-liquid separator 26. Separator26 and the other vapor-liquid separators of FIGS. 1 and 2 arecylindrical vertically oriented vessels that may contain internals toassist phase separation. Horizontally oriented vessels and indeed anysuitable phase separation device may be used for these vapor-liquidseparators. A vapor phase enriched in isobutane and containing propane,ethane, methane, and hydrogen chloride is recovered from separator 26 inline 28. (Hydrogen may be present, but if so it is present only in smallquantities compared to hydrogen chloride.) This vapor phase is deemed arefrigerant for the process. Compressor 32 compresses this vapor phaseand discharges it into line 34. Water-cooled condenser 36 condenses aportion of the compressed stream in line 34, and a two-phasevapor-liquid mixture flows through line 38 to exchanger 22. In exchanger22, further condensation of isobutane occurs. The refrigerant is cooledin exchanger 22 to such an extent that, at the pressure of the chilledrecycle stream recovered from the outlet of exchanger 22, a significantportion of the hydrogen chloride is condensed and is present dissolvedin solution in the isobutane-rich liquid phase in line 40.

The chilled recycle stream flowing in line 40 contains paraffins lighterthan the alkylation substrate and/or hydrogen chloride. Hydrogen, ifany, is present only in small quantities relative to hydrogen chloride.Since these components do not react to any significant extent in thealkylation reactor, recycling all of the C₁–C₃ paraffins and hydrogenwould allow them to accumulate in the refrigerant to concentrations thatare not condensable. These components are preferably purged from therefrigerant from any convenient location. One possibility is to vent aslipstream from line 28. Although this option would save the cost ofcompressing the slipstream in compressor 32, the compressor suctionpressure might be too low as a practical matter for the slipstream to beuseful elsewhere. Two other possibilities are to vent a slipstream fromlines 34 or 38. While these locations would reject the slipstream at ahigher and more useful pressure, they would prevent the slipstream fromexchanging its heat with the reactor effluent in exchanger 22, therebyreducing the vaporization of the reactor effluent and thus the flow ofrefrigerant itself. These two possibilities, however, are not equivalentin terms of the duty of condenser 36. (Condenser 36 and/or exchanger 22may also have a normally closed vent, which can be opened to remove“noncondensables”.) If the chilled recycle stream in line 40 is atwo-phase mixture, a fourth possibility is to pass some or all of thestream flowing in line 40 to a vapor-liquid separator (not shown),forming a vapor phase and a liquid phase, rejecting the resulting vaporphase from the process, and routing the resulting liquid phase to pump42. This would help prevent cavitation in pump 42 and would minimizeisobutane losses by concentrating the C₁–C₃ paraffins and/or hydrogen inthe vented stream. On the other hand if the chilled recycle stream inline 40 is a single liquid phase, it may be preferred to pass aslipstream from line 44 to product recovery section 88. There, theslipstream could be charged to a flash drum or a depropanizerdistillation column (not shown). The flash drum or depropanizer wouldconcentrate the C₁–C₃ paraffins and/or hydrogen in its overhead streamto be rejected from the process in line 90, and the isobutane would berecovered in its bottom stream to be recycled to the alkylation reactor10 through line 92 or through line 12 (by way of a line not shown). Theproduct recovery section 88 could include both a flash drum and adepropanizer. The selection of the optimum from among these options iswithin the skill of a person of ordinary skill in the art.

Regardless of the location chosen for purging the C₁–C₃ paraffins andhydrogen chloride, most or all of the refrigerant flows through line 40and is pumped by pump 42 to the pressure required for charging to eitherthe alkylation reactor 10 or the product recovery section 88. Except forany slipstream to product recovery section 88, pump 42's dischargestream flows through line 44, combines with the stream flowing in line94, and returns to the alkylation reactor via line 14.

The other portion of the reactor effluent flows through line 62 andflashes across expansion valve 64, which lowers this portion's pressureand temperature. This flashed portion is also a two-phase vapor-liquidmixture that flows through line 66 to exchanger 68. Using indirect heatexchange, this flashed portion of the reactor effluent removes heat fromthe isobutane-containing recycle stream flowing through line 92. Whilecooling the recycle stream before its return to the alkylation reactor10, this heat exchange heats and/or vaporizes some of this portion ofthe reactor effluent. The effluent of exchanger 68 flows through line70, combines with the portion of the effluent flowing in line 24, flowsthrough line 25, and enters separator 26.

The liquid phase recovered from separator 26 in line 80 containsalkylate and usually some isobutane too, but it is depleted in isobutanerelative to the stream flowing in line 25. This liquid phase flows toproduct recovery section 88. Although not shown, product recoverysection 88 typically consists of the previously mentioned flash drum ordepropanizer distillation column as well as a deisobutanizerdistillation column (not shown), which is commonly called anisostripper. The liquid phase in line 80 and a field butanes stream,which consists of a mixture of normal butane and isobutane, in line 86are charged to the isostripper. A normal butane stream in line 84, analkylate product stream in line 82, and the isobutane stream in line 92(which contains both fresh isobutane charged via line 86 and recycleisobutane) are recovered from the isostripper. Optionally, some or allof the normal butane may be recovered in line 82.

The isobutane in the stream in line 92 is recycled to the alkylationreactor 10 via exchanger 68, line 94, and line 14. This route cools therecycle and fresh isobutane in exchanger 68 before charging it toalkylation reactor 10. The stream in line 14 is at a temperature ofgenerally from about −4 to about 27° C. (25 to 80° F.). Although notshown in FIG. 1, the streams in lines 92 and 12 may be cooled by heatexchange with some or all of the liquid phase flowing in line 80.

Turning now to FIG. 2, FIG. 2 shows three stages of compression, whereasFIG. 1 shows only one stage. Because FIG. 2 is similar to FIG. 1,similar items in both FIGS. 1 and 2 have been given similar (but notidentical) numbering. To avoid needless repetition, these similar itemsare not described in detail again. The butene feedstock enters reactor310 through line 312. An isobutane-containing stream enters reactor 310through line 314. The alkylation reactor effluent flows through line 316and flashes across valve 318. The resulting vapor-liquid mixture flowsthrough line 320 to refrigerant heat exchanger 322 where it is furthervaporized as it cools the stream in line 338. The exchanger effluentflows through line 324 and enters vapor-liquid separator 326. A vaporphase enriched in isobutane and containing C₁–C₃ paraffins and hydrogenchloride is recovered from separator 326 in line 328. This vapor phasecombines with the stream flowing in line 360 to form the stream in line330, which functions as the refrigerant in the process. Compressor 332compresses this stream and discharges it into line 334. Water-cooledcondenser 336 condenses a portion of the stream in line 334, and avapor-liquid mixture flows through line 338 to exchanger 322 whereessentially complete condensation occurs. All of the hydrogen chlorideis in solution in the isobutane-rich liquid phase in line 340.

All of the refrigerant flows through line 340 to pump 342, which pumpsthe refrigerant into line 344. A line (not shown) carries a slipstreamof pump 342's discharge stream from line 344 to product recovery section388. The bulk of pump 342's discharge stream combines with the streamflowing in line 392, flows through line 394, is cooled in recycle heatexchanger 368, and returns to the alkylation reactor 310 via line 314.

The liquid phase recovered from separator 326 in line 346 containsalkylate and is depleted in isobutane compared to the stream flowing inline 324. The liquid phase flashes across expansion valve 348, whichdrops the liquid phase's pressure and temperature and forms a two-phasemixture that flows through line 350 to vapor-liquid separator 352. Avapor phase enriched in isobutane and containing methane, ethane,propane, and hydrogen chloride is recovered from separator 352 in line354. This vapor phase combines with the stream flowing in line 378 toform the stream in line 356. Compressor 358 compresses this stream anddischarges it into line 360.

The liquid phase recovered from separator 352 in line 362 containsalkylate and is depleted in isobutane compared to the stream flowing inline 350. The liquid phase flashes across expansion valve 364, whichdrops the liquid phase's pressure and temperature and forms a two-phasemixture that flows through line 366 to exchanger 368. This flashedliquid phase cools the isobutane-containing stream flowing in line 394and passes as a vapor-liquid mixture through line 370 to vapor-liquidseparator 372. A vapor phase enriched in isobutane and containingmethane, ethane, propane, and hydrogen chloride is recovered fromseparator 372 in line 374. Compressor 376 compresses this stream anddischarges it into line 378. A liquid phase containing alkylate anddepleted in isobutane is recovered from separator 372 in line 380.

The liquid phase in line 380 flows to product recovery section 388. Line386 carries a field butanes stream carrying isobutane feedstock to theproduct recovery section 388. A light stream comprising methane, ethane,propane, and hydrogen chloride is rejected from the process in line 390.A normal butane stream in line 384, an alkylate product stream in line382, and the isobutane-containing stream (which contains both fresh andrecycle isobutane) in line 392 are recovered from the product recoverysection.

A variation of the embodiment in FIG. 2 uses two stages of compression.Thus, valve 348, line 350, separator 352, and line 362 are eliminated,so that the stream in line 346 flows directly to valve 364. Line 354,line 356, compressor 358, and line 360 are deleted also, and the streamin line 378 flows to the junction of lines 328 and 330.

1. An alkylation process comprising a) alkylating an alkylationsubstrate with an alkylating agent to form alkylate in a reactor; b)recovering from the reactor a reactor effluent comprising the alkylateand the alkylation substrate; c) flashing at least a portion of thereactor effluent to form a refrigerant exchanger feed comprising thealkylate and the alkylation substrate, wherein the refrigerant exchangerfeed has the same composition as the at least a portion of the reactoreffluent; d) heating at least a portion of the refrigerant exchangerfeed in a refrigerant heat exchanger and recovering from the refrigerantheat exchanger a refrigerant exchanger effluent comprising the alkylateand the alkylation substrate; e) passing at least a portion of therefrigerant exchanger effluent to an effluent vapor-liquid separator andrecovering from the effluent vapor-liquid separator a vapor phasecomprising the alkylation substrate and a liquid phase comprising thealkylate; f) compressing the vapor phase to form a compressed streamcomprising the alkylation substrate; g) at least partially condensing atleast a portion of the compressed stream to form a condensed streamcomprising the alkylation substrate; h) indirectly exchanging heat inthe refrigerant heat exchanger from at least a portion of the condensedstream to the at least a portion of the refrigerant exchanger feed toform a chilled recycle stream comprising the alkylation substrate; i)recycling at least a portion of the chilled recycle stream to thereactor; and j) recovering the alkylate from the liquid phase.
 2. Theprocess of claim 1 further characterized in that the at least a portionof the condensed stream at least partially condenses in the refrigerantheat exchanger, the chilled recycle stream comprises a condensed phase,and the recycling of the at least a portion of the chilled recyclestream comprises recycling the condensed phase.
 3. The process of claim2 further characterized in that the chilled recycle stream comprises ahydrogen halide, and the condensed phase comprises at least 99% of thehydrogen halide in the chilled recycle stream.
 4. The process of claim 3wherein the hydrogen halide comprises hydrogen chloride.
 5. The processof claim 1 further characterized in that the alkylating occurs in thepresence of a solid catalyst.
 6. The process of claim 1 wherein thereactor is a transport reactor.
 7. The process of claim 6 wherein thetransport reactor is a riser-reactor.
 8. The process of claim 1 furthercharacterized in that the at least a portion of the refrigerantexchanger effluent is separated at separation conditions comprising apressure of from about 0 to about 483 kPa(g) and a temperature of fromabout −9 to about 32° C.
 9. The process of claim 1 further characterizedin that the effluent vapor-liquid separator operates at a phaseseparation temperature and the chilled recycle stream is at a chilledrecycle temperature of from about 2 to about 11° C. greater than thephase separation temperature.
 10. The process of claim 1 furthercharacterized in that the vapor phase comprises a light component havingfewer carbon atoms than the alkylation substrate, a reject streamcomprising the light component is formed from a stream selected from thegroup consisting of the vapor phase, the compressed stream, thecondensed stream, and the chilled recycle stream, and the lightcomponent in the reject stream is rejected from the process.
 11. Theprocess of claim 1 further characterized in that the at least a portionof the refrigerant exchanger feed comprises a hydrogen halide.
 12. Analkylation process comprising a) alkylating an alkylation substrate withan alkylating agent to form alkylate in a reactor; b) recovering fromthe reactor a reactor effluent comprising the alkylate and thealkylation substrate; c) depressuring at least a portion of the reactoreffluent, wherein the at least a portion of the reactor effluent afterthe depressuring has the same composition as the reactor effluent; d)heating the at least a portion of the reactor effluent after thedepressuring in a refrigerant heat exchanger and recovering from therefrigerant heat exchanger a refrigerant exchanger effluent comprisingthe alkylate and the alkylation substrate; e) passing at least a portionof the refrigerant exchanger effluent to an effluent vapor-liquidseparator and recovering from the effluent vapor-liquid separator avapor phase comprising the alkylation substrate and a liquid phasecomprising the alkylate; f) compressing the vapor phase to form acompressed stream comprising the alkylation substrate; g) at leastpartially condensing at least a portion of the compressed stream to forma condensed stream comprising the alkylation substrate; h) indirectlyexchanging heat in the refrigerant heat exchanger from at least aportion of the condensed stream to the at least a portion of the reactoreffluent to form a chilled recycle stream comprising the alkylationsubstrate; i) recycling at least a portion of the chilled recycle streamto the reactor; and j) recovering the alkylate from the liquid phase.